1. Field of the Invention
The present invention relates to a method of and an apparatus for expanding a system bus.
2. Description of the Related Art
A system for expanding a system bus by using a bus expansion adapter is known. In the system a channel unit connected to the system bus and a channel unit connected to a system bus expanded by the bus expansion adapter, i.e., an expansion system bus, are equally treated from the viewpoint of the overall system. That is, a memory request output from the channel unit connected to the expansion system bus is directly transferred onto the system bus through the bus expansion adapter. For this reason, a channel unit connected to the expansion system bus can perform input/output control between a main memory and an input/output unit as if it were connected to the system bus.
If, however, memory requests are frequently generated from a plurality of channel units connected to the expansion system bus, the load of the system bus is increased. As a result, queue signals are generated from these channel units, and the system throughput is decreased.